Diesel engines, in the presence of combustible gases in the atmosphere, occasionally enter a runaway condition in which the engine, without a proper device to mitigate this problem, can enter an uncontrolled acceleration. In this condition, the engine experiences combustion and, if not stopped, the engine can reach speeds that can result in destruction and/or catastrophic engine failure, and personal injury. There are a number of causes of runaway including, for example, a faulty engine governor, engine overheating or the ingestion of unregulated hydrocarbons into the combustion chamber. Such hydrocarbons may be from an external source such as airborne gas, or from the engine itself due to a malfunction such as failure of turbocharger oil seals.
One conventional way to stop a runaway diesel engine involves blocking the air supply to the combustion chamber of the engine. Once deprived of oxygen, the runaway ceases. Accordingly, safety valves which cut off the air supply to the engine have been developed to shut off the engine in such a situation.
Amot Controls, Corp., the assignee of the subject invention, offers various automatic engine overspeed shutdown valves under its Chalwyn brand. Examples of such valves are those designated as the Chalwyn Bendix Range D-Valves (D29 to D80). Those valves constitute a range of small spring loaded poppet valves, each of which is arranged for placement in the air intake to the engine. Such valves employ a valve disc that designed to automatically stop an engine by closing down the air intake, e.g., the valve disc intimately engaging a valve seat, should excessive engine overspeeding occur which action increases the speed and force of the airflow through the air passageway to the engine. The closing force on the valve is provided by the intake air flow passing through the valve which operates to overcome a bias provided by a spring in the valve. As the air flow increases, the closing force builds up. This is resisted by the bias of the spring, the pre-load of which is adjustable, such that at a given air flow the resulting force overcomes the spring resistance and causes the valve to close, thus cutting off the air supply to the combustion chamber, thereby starving the engine of oxygen such that the engine stalls. Once closed, the valve will not reset to the open condition until the engine stops. This type of valve may be fitted to either naturally aspirated or turbocharged engines.
While such prior art shutoff valves have proved suitable for their intended purposes, they nevertheless leave something to be desired from the standpoint of being resistant to sticking closed once they have operated to shut off the engine. Thus, a need exists for a more stick-resistant engine overspeed shut-down valve, particularly one that is relatively simple in construction. The present invention addresses that need. All references cited herein are incorporated herein by reference in their entireties.